Artificial materials and process of making the same



Patented June 23, 1936 UNITED STATES ARTIFICIAL MATERIALS ANI) PROCESS OF MAKING THE SAME Robert Pierce Roberts, Edgar Bertie Johnson,

and Louis Wilfred Gregory,

Spondon, near Derby, England, assignors to Celanese Corporation of America, a corporation of Delaware N 0 Drawing.

Application March 2, 1932, Serial No. 596,406. In Great Britain April 28, 1931 11 Claims.

This invention relates to the production of filaments, ribbons, films and the like by dryspinning processes.

According to the present invention, in the production of such materials there are employed spinning solutions which, in addition to the relatively volatile solvent in which the base of the spinning solution is dissolved, contain non-solvents or precipitants for said base, and the extruded spinning solutions are subjected during their conversion into filaments and the like to the vapour of substances having a solvent or swelling action on the base. Thus, for example, we may spin a solution of cellulose acetate in acetone containing a xylene or other non-solvent for cellulose acetate under such conditions that a stream of acetone vapour is directed on to the materials in the vicinity of the spinning jets. In this way filaments and the like may be produced having a central core of precipitated material, that is, material exhibiting. a discontinuous or granular structure, and an outer layer or skin of material having a more or less continuous gel structure.

The process of the invention is particularly applicable to the production of filaments and the like from cellulose acetate. Other derivatives of cellulose may however, be employed, for example esters such as cellulose nitrate, cellulose formate, propionate, or butyrate, ethers such as ethyl, methyl or benzyl cellulose, mixed esters, e. g. cellulose nitro-acetate, and ether-esters.

Any suitable volatile solvent may be employed in making up the spinning solution. Among suitable solvents for cellulose acetate mention may be made of acetone, and mixtures of ethylene and methylene dichlorides with ethyl and methyl alcohols. We prefer to employ a solution of cellulose acetate in acetone. The concentration of the cellulose derivative in the spinning solution will naturally depend upon the nature and pro portions of the particular solvent and the nonsolvent employed. In general, solutions containing an amount of cellulose acetate ranging from 15% to 30%, and particularly solutions containing about 25%, are preferred. Where relatively concentrated solutions of the cellulose derivative are employed the viscosity may be reduced by any suitable means in order to facilitate spinning. For example the spinning solution may be supplied at a temperature above atmospheric temperature, or its viscosity may be decreased by the addition of suitable substances, such as the electrolytes of U. S; appli cation S. No. 401,625 filed 2 2nd october, 192i).

' agents for the cellulosederivative, the vapours The non-solvent should preferably have at the temperature of spinning a substantially lower vapourpressure than that of the volatile solvent. Among non-solvents for cellulose acetate which may be employed in carrying out the invention mention may be made of liquid aromatic hydrocarbons such, for example, as the xylenes or toluene, kerosene, ligroin or other petrol fractions of low volatility, halogenated hydrocarbons, e. g. carbon tetrachloride', and alcohols which are strong precipitants for the cellulose acetate.

The proportion of non-solvent present in the spinning solution may vary within wide limits, provided that it is not sufiicient to cause precipitation of the base before spinning, for example it may be, and preferably is, present in such quantity as would produce a precipitated product during a normal spinning process.

The solvent or swelling agent, the vapour of which is applied to the materials emerging from the spinning jets or dies,"may be of any suitable nature. Preferably relatively volatile solvents are emp1oyed,'and the best results appear to be obtained when the solvent applied in this way is the same as that employed in the spinning solution. Thus in working with solutions of cellulose acetate in acetone, excellent results are obtained by projecting a current of acetone vapour on to the materials in the neighbourhood of the jets. As examples of other solvents or swelling of which may be employed'with advantage in the process of the invention, mention may be made of methyl ethyl ketone, dimethyl glycol, ethylene dichloride, acetic acid, formic acid, ethyl formate, methyl formate, methyl acetate, and of acetaldehyde, formaldehyde and other relatively low boiling solvents. The solvent or swelling agent employed in any particular case should be chosen'with due regard to the temperature at 40 which spinning is to be effected. The solvent vapourmay or may not be 'mixed with air or other inert gas, and may if desired be diluted with vapours of non-solvents.

1 The vapour maybe applied by any convenient means. Thus, for example, it may be supplied to a perforated ring supported in the neighbourhood of the spinning jets, the arrangement being such that a stream of vapour is projected through the perforations on to the materials issuing from the jets. Again, the vapour may be sprayed or otherwise caused to issue through the perforations in one or a number of tubes situated along the length of the path of the n'laterials through the spinning cell. Various means of subjecting filaments and the like to the action of gases or vapours during the early stages of their formation are illustrated in U. S. applications S. Nos. 463,658 filed 25th June, 1930 which has become Patent 1,950,025, 463,932 filed 26th June, 1930 which has become Patent 1,950,026, and 382,907 filed 2nd August, 1929 which has become Patent 1,934,618. The apparatus described and claimed in the last-named specificationis particularly suitable for the application of the solvent vapours according to the present invention. If desired, the effect of the solvent vapours on the filaments may be prolonged and intensified by surrounding the spinning jets or dies with a shield or other device designed to cause all or a large pro,- portion of the evaporative medium to flow past the jets. The production of this effect by the use of collector devices is illustrated in U. S. applications S. Nos. 236,448 filed 29th November, 1927, which has become Patent 1,814,468, 311,213 filed 8th- October, 1928, 311,214 filed 8th October, 1928, and'405,784 filed'8th November, 1929, which has become Patent 1,942,540.

The'conditions of spinning, for example temperature and speed of drawing off, may be such that at least a part and preferably the greater part of the non-solvent is removed during the progress of the materials through the spinning cell. It is not, however, necessary to spin under such conditions that the materials emerging from the cell are free from the non-solvent. When the process is 'carried'out so that the materials emerging from the cell still contain a proportion of the non-solvent, this may be removed by a suitable. after-treatment, for example by passing the materials through a liquidtreating agent, or over a heated surface, or through a heated atmosphere. The particular method adopted may depend upon the characteristics of the particular non-solvent employed. Where a non-solvent of relatively high boiling point is employed a liquid treatment. is to be preferred; The liquid used should not havea pronounced solvent 'efiect on the cellulose, derivative. Liquids having a swelling or softening effect thereon are not however objectionable and may in. fact be preferable where, for example, as described below; a stretch is .to be imparted to the materials continuously with their manufacture.

By suitably effecting the removal of the nonsolvent liquid from the materials, hollow or more hollow filaments or the like may be obtained.

For example, rapid evaporation may be promoted in the lower part of the spinning cell, either by passing the materials through a region maintained, by means of heating devices, at a relatively elevated temperature, which may advantageously be approximately that of the boiling point of the non-solvent or even highermrby increasing the rate of fiow of the evaporative medium in the neighbourhood of thematerials; Suitable methods of carrying out the latter operationv are disclosed in U. S. applications'S'. Nos. 236,448, 311,213, 311,214 and 405,784. If desired these two methods of producing a rapid evap-- oration may be combined, as, for example, by providing collector devices with heating arrangements, as described in U. Sapplication S. No. 236,448.

The following example of a method of carrying out the invention is given by way of illustration, but'it is to be clearly understood that the invention is in no way limitedthereto.

Example A 25% solution of cellulose acetate in a solvent mixture consisting of 78 parts by weight of acetone and 22 parts by weight of xylene is spun, according to dry-spinningmethods, into a cell into which 4 cu. ft. per minute of acetone-laden air are introduced in the neighbourhood of the jet. This may be conveniently effected by means of anyof the. types of apparatus described in .U. S. application S. No. 382,907, the air being previously passed through a vessel containing acetone maintained near its boiling point.

As stated above, by the process of the present invention materials having a central core of precipitated material surrounded by an outer layer having a more or less continuous gel structure may be obtained, while in general they are also characterized by increased covering power and a low specific gravity, for example 1.0 or even less.

The materials may, continuously with their production according to the process of the invention, be subjected to any suitable treatment designed to modify their strength, lustre or other physical properties. For example, a stretch may be imparted to the materials during their passage through the spinning cell and/or after their emergence therefrom. Thus the materials may be stretched by the action of a rapid current of air or. other gaseous medium produced in the spinning cell by means of suitable ejectors or other devices as described in U. S. application S. No. 390,354 filed 4th September, 1929. Again, in applyinga stretch to the materials advantage may be taken of the principles illustrated in British application No. 9428/31 filed 27th March, 1931 which has become Patent 375,425, wherein the travel of the materials is retarded by a counter-current of air or other fluid applied at any point along the path. Further, a stretch may be imparted by passing the filaments, threads or the like over' two or a series of rotating members of successively increasing peripheral speeds, or by running the bobbin, swift or other collecting device at a suitable speed.- With a view to facilitating the stretching of. the materials, suitable swelling or softening agents may be applied thereto, for example, solvents or swelling agents in liquid form may be applied to the materials by means of baths, padding. rolls, wicks, and the like. Such solvents or swelling agents should preferably be of boiling point sufficiently high tobe retained by the materials for some distance along their path. To avoid rapid loss by evaporation it is preferable to employ softening liquids of relatively high boiling point, for example cyclo-hexanone, methyl cyclohexanone, diacetone alcohol, phenol, ethyl lactate, diacetin or triacetin. 1

Materials of dull or still duller lustre .may be produced by incorporating in the spinning solution finely divided pigments or other substances, preferably of high, melting point, in quantities greater than are soluble in the cellulose derivative, asdescribed in U. S. applications S. Nos. 444,622 filed 15th April, 1930, 464,122 filed 26th June, 1930, 473,781 filed 7th August, 1930, and 473,782filed 7th August, 1930. Again, pigments may be produced in the; materials by reaction therein between two substances. The term solvent as used in the claims with respect to the agent present in the evaporative atmosphere isto be understood as including swelling agents.

What we claim and desire to secure by Letters Patent is':

1. Process for the production of artificial filaments, threads, ribbons, films and the like, which comprises forming a solution of a base material in a solvent mixture comprising a solvent and a non-solvent for the base material in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the base material would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of a solvent for the base material in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

2. Process for the production of artificial filaments, threads, ribbons, films and the like, which comprises forming a solution of an organic derivative of cellulose in a solvent mixture comprising a. solvent and a non-solvent for the organic derivative of cellulose in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the organic derivative of cellulose would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of a solvent for the organic derivative of cellulose in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

3. Process for the production of artificial filaments, threads, ribbons, films and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising a volatile solvent and a less volatile non-solvent for the cellulose acetate in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the cellulose acetate would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of a solvent for the cellulose acetate in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

4. Process for the production of artificial filaments, threads, ribbons and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising a solvent and a strongly-acting precipitant for the cellulose acetate in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the cellulose acetate would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of a solvent for the cellulose acetate in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

5. Process for the production of artificial filaments, threads, ribbons and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising acetone and a less volatile non-solvent for the cellulose acetate in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the cellulose acetate would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of a solvent for the cellulose acetate in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

6. Process for the production of artificial fila ments, threads, ribbons, films and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising a solvent and a non-solvent for the cellulose acetate in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the cellulose acetate would be precipitated, and extruding the said solution through suitable orifices into an evaporative atmosphere which already contains the vapor of the said solvent for the cellulose acetate in amount sufficient to give a continuous gel structure to the surface only of the extruded products.

7. Process for the production of artificial filaments, threads, ribbons, films and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising acetone and xylene in such proportions that before all the said mixture would evaporate in a substantially solvent-free atmosphere the cellulose acetate would be precipitated, and extruding the said solution through'suitable orifices into air which already contains the vapor of acetone in amount sufiicient to give a continuous gel structure to the surface only of the extruded products.

8. Process for the production of artificial filaments, threads, ribbons, films and the like, which comprises forming a solution of cellulose acetate in a solvent mixture comprising '78 parts by weight of acetone and 22 parts by weight of xylene, and extruding the said solution through suitable orifices into air which already contains the vapor of acetone in amount sufficient to give a continuous gel structure to the surface only of the extruded products.

9. Artificial filaments, threads, ribbons and the like having a precipitated core and an outer layer of continuous structure.

10. Artificial filaments, threads, ribbons and the like having a basis of an organic derivative of cellulose and having a precipitated core and an outer layer of continuous structure.

11. Artificial filaments, threads, ribbons and the like having a basis of cellulose acetate and having a precipitated core and an outer layer-of continuous structure.

ROBERT PIERCE ROBERTS. EDGAR BERTIE JOHNSON. LOUIS WILFRED GREGORY. 

